Wavelength encoded single-shot high-spatiotemporal resolution all-optical probe

Abstract

The laser probe method is one of the main techniques for capturing ultrafast dynamic processes and has extensive applications in fields such as plasma physics, photochemistry, and biomedical science. In this paper, a time-wavelength encoding optical probe generation scheme is proposed, which uses cascaded frequency doubling crystals with different phasematching angles and independent delay lines to achieve time-wavelength encoding. This method offers single-shot high spatiotemporal resolution, high frame rate, a wide range of adjustable time windows. The temporal resolution of the optical probe depends on the pulse width of the second harmonic, which can be adjusted by changing the phase-matching angle of the frequency doubling crystal. The time window of the optical probe is only related to the change in the delay line, which can be adjusted by changing the length of the delay line. Therefore, the time resolution and time window of the optical probe are independent of each other. An optical probe generation system was constructed with 247 fs temporal resolution, 4 μm spatial resolution, 4.05 THz maximal frame rate, and an adjustable time window from sub-picosecond to 3 ns. The threedimensional spatiotemporal evolution process of plasma filaments was captured within a single shot using the optical probe. The experimental results showed that the ionization front of the plasma propagated forward at a velocity of (2.963 ± 0.024) × 10<sup>8</sup> <i>m</i>/<i>s</i>,which was consistent with the theoretical prediction. This demonstrated the feasibility of using the probe for capturing ultrafast events. In the discussion, we analyzed that the key parameters of the optical probe can reach a maximum frame rate of 35.7 THz, a maximum time resolution of 28 fs, and a time window range that can be adjusted from hundreds of femtoseconds to tens of nanoseconds. Finally, the optimal design parameters of the optical probe are given for different application scenarios. The optical probe generation scheme has good scalability and versatility, and can be combined with any wavelength decoding device, diffraction imaging, holographic imaging, tomography scanning, and other technologies. The high spatiotemporal resolution of the optical probe and the independent adjustability of its parameters provide a feasible solution for single-shot high spatiotemporal resolution captures of ultrafast dynamic processes at multiple time scales.